1. Field of the Invention
The present invention relates to an image information processing apparatus, an image information processing method, and a program, and more particularly, to an image information processing apparatus, an image information processing method, and a program that are suitably used in a case where three-dimensional volume data of a sample is generated based on two-dimensional projection image data obtained by irradiating a single scan cone beam of an X-ray etc., for instance, to the sample.
2. Description of Related Art
In recent years, a three-dimensional CT (Computerized Tomography) system capable of acquiring sectional image data of a sample is employed in fields of medical treatments or industries etc. In the three-dimensional CT system, a transmittable energy of an electromagnetic wave such as an X-ray and a γ-ray, and an ultrasonic wave etc., for instance, is irradiated to the sample to acquire (capture) projection image data based on light waves transmitted through the sample. Then, volume data that is specified in the form of a rectangular parallelepiped lattice of a size enough to cover the sample and is composed of more than one voxel supposed to hold an X-ray absorption coefficient value of each sampling point is calculated based on more than one projection image data obtained by capturing an image of the sample from a full circumference direction, leading to a generation of the sectional image data of the sample in an arbitrary direction based on the calculated volume data.
FIG. 10 illustrates one instance of a configuration of a related art three-dimensional CT system. The illustrated three-dimensional CT system is composed of an X-ray source 2 that irradiates a single scan beam of the X-ray to a sample 1, a rotator 3 that rotates the mounted sample 1 in 360 degrees, a photo detecting section 4 that detects the X-ray having transmitted through the sample 1 to generate projection image data, and an image processing apparatus 5 that calculates volume data of the sample 1 based on more than one projection image data obtained from the full circumferential direction of the sample 1, and further generates the sectional image data. It is noted that the above system normally takes an arrangement such that a plane of the rotator 3 is orthogonal to a detection surface of the photo detecting section 4, and a rotation axis of the rotator 3 extends in parallel to one coordinate axis of the detection surface of the photo detecting section 4. Further, the above system is also available in the form of a system configured to provide no rotation of the sample 1 in a mounted condition on the rotator 3, but, fix the sample 1 to permit the X-ray source 2 and the photo detecting section 4 to rotate around the sample 1.
It is noted that a method (which is hereinafter also referred to as a three-dimensional reconfiguration method) of generating, based on more than one projection image data, the volume data corresponding to the sample 1 is described in “Reconfiguration of Three-dimensional X-ray CT image using Distributed memory-type multiprocessor system” by Toru SASAKI and one other, the ninth issue of Information Processing Society thesis journal in Vol. 38 in 1997, for instance.
By the way, as shown in FIG. 11, the related art three-dimensional reconfiguration method has been based on that a projection image of the sample 1 is acquired, with an optical axis (a perpendicular from the X-ray source 2 to the photo detecting section 4) arranged to be perpendicular to the rotation axis of the rotator 3 (which is hereinafter referred to as a related art arrangement).
The related art arrangement, when using a thin plate-shaped object (which is also hereinafter referred to as a plate-shaped sample 1) as the sample 1, is supposed to create an easily transmitting condition of the X-ray (as shown in FIGS. 11A and 11B, for instance) and a hardly transmitting condition or no transmitting condition (as shown in FIGS. 12A and 12B) of the X-ray depending on a difference in a rotation angle of the rotator 3, in which case, a difference between these conditions brings about a difference in image quality of the projection image, resulting in a problem that the three-dimensionally reconfigured volume data obtained using more than one projection image having a different image quality easily yields artifacts.
Further, the related art arrangement, when bringing the rotator 3 close to the X-ray source 2 as shown in FIGS. 13A and 13B, for instance, in an attempt to magnify a size of the plate-shaped sample 1 in the projection image, causes the sample 1 to strike against the X-ray source 2 depending on the rotation angle of the rotator 3, resulting in a problem of difficulty in attainment of a desired magnification.
To solve the above problems, there is proposed, as shown in FIG. 14, for instance, a method of taking an arrangement such that the rotation axis of the rotator 3 is inclined at an angle with the optical axis, without being limited to a perpendicular arrangement. For example, such a method is disclosed in Japanese Patent Laid-open No. 2003-260049 (Patent Document 1). According to the above method, the magnification of the sample 1 in the projection image may be increased, as compared with the related art arrangement. Further, a surface of the plate-shaped sample 1 and the optical axis may be arranged without reaching an alignment, so that there is also an effect that the hardly transmitting condition or no transmitting condition of the X-ray is hard to be created. Thus, the method of taking the arrangement having an inclined angle between the rotation axis of the rotator and the optical axis is given attention as an effective nondestructive inspection method of the plate-shaped sample.